The Celtics, who are off until hosting the Orlando Magic Sunday at TD Garden, have lost plenty lately — four straight and 19 of their last 22. At 15-33, they have the NBA’s third-worst record.

The Celtics are also 0-6 with Rondo in the lineup this season, proof that their issues run deep, so much so that he alone cannot turn around a ship that is heading for a likely lottery draft pick.

Of course, even though Rondo is back in uniform, he’s not in full form — not yet.

And while Rondo has learned to be patient throughout the past year as he has worked diligently to return from a knee injury, it still isn’t easy for him to be on the court and not be his old self, especially when he knows his old self could help his team win.

“I get frustrated,” said the ultracompetitive Rondo. “I’ve been frustrated my entire career. I always want to win. I hate losing — any games we lose, anything I play.”

Rondo has steadily improved over his six games. He has averaged seven assists over the last three, and he was within reach of a triple-double last Sunday against Brooklyn, finishing with 13 points, 8 rebounds, and 8 assists in 30 minutes.

But for now, Rondo, who is playing on a minutes restriction and has twice sat out the second game of back-to-back sets to rest, isn’t right. And more often than not in those six games, the Celtics’ captain and the best player on the roster has looked rusty, as was to be expected.

He’s shooting just 28 percent from the floor and has looked out of synch with his teammates, many of whom are new this season.

“I’m just trying to find ways to keep meshing with these guys and continuing to learn one another and make the right plays in the fourth quarter,” Rondo said.

This reacclimation period is difficult, because he’s finally back on the court after nearly a year away, but he still isn’t playing the way he did when he left.

“It’s part of the process,” Rondo said. “I’ll be fine. I’m competitive. I want to win. I hate losing. But it’s not the end of the world. I’m still doing what I love to do.”

His outlook speaks to his improved patience, which is quite a feat for Rondo. In fact, earlier this month, when the Celtics paid a visit to Doc Rivers’s Los Angeles Clippers, the former Celtics coach laughed at the idea of Rondo being patient throughout the rehab process.

“Rondo, patient?” Rivers said, a half-kidding nod to the fact that the two words mix together like oil and water. “You want to get back, and especially the better the player. A Rondo, a Derrick Rose, patience is not something good for them. They want it now.”

Yet the injury and rehab forced Rondo to accept patience, and he believes that in the long run, the process, including this period of adjustment now that he’s back in the lineup, should benefit him.

“Hopefully,” he said. “Hopefully this is just temporary. But I think so. It’s a very humbling experience, not being able to do what you love for a long period of time at the level you want to do. I’m more grateful for the opportunity to play the game, regardless of the outcome or how I play. I’m waking up every day doing what I love to do and not enough people are fortunate enough to do that. It’s a game. I’m very competitive. But at the end of the day, it’s just a small part of the life.”

The one-year anniversary of his injury, the torn anterior cruciate ligament he suffered Jan. 25, 2013, against Atlanta, passed last weekend.

“I don’t think about it too much,” Rondo said. “It’s all about the future. That happened in the past. Now I’m just moving forward, making progress every day.”

In fact, Rondo, who will turn 28 on Feb. 22, added that the injury and the rehabilitation changed his habits, in a positive manner.

“I think I work harder in the weight room,” he said. “I’m more focused in certain areas. I’m young, and when you’re young and you get hurt, you feel [invincible]. Just like when I got hurt, I thought I would bounce back the next day. But I have to do a better job of taking care of my body, proper treatment. I can’t just do it like I used to.”

For now, he’s working his way back, as he has done in various degrees since he injured his knee. It’s a process that can’t be rushed, even if Rondo would like to wake up tomorrow and be the player he was before he got hurt.

But as Rondo said, even when he is his old self again, he alone is not enough to rescue these Celtics. That would require not just one, but several superhero-like feats. And while Rondo has played like a superhero before, his injury proved that, above all else, he is still human.